1. Field of the Invention
The present invention generally relates to a brushless motor, and in particular to a connection construction between a rotor frame, a turntable, a hub, a rotor boss, and the like, and a shaft of a brushless motor rotationally driven primarily with an information-recordable/reproducible disk such as a compact disk, a video disk, or a magnetic disk being mounted on the turntable, hub, or the like. Alternatively, the present invention relates to a connection construction between a rotor frame, a turntable, a hub, a rotor boss, and the like, and a shaft of a brushless motor rotationally driven with a load such as a rotational polygon mirror mounted thereon.
2. Description of the Prior Art
A conventional brushless motor is disclosed in, for example, Japanese Patent Unexamined Laid-Open Publication 8-289523 (published in 1996). FIG. 8 shows a construction of the conventional brushless motor. FIG. 8. is a cross-sectional view of an embodiment of the conventional brushless motor. In FIG. 8, numeral 71 denotes a shaft for transmitting rotation. Numeral 72 denotes a rotor frame in which a ringular magnet 73 circumferentially multipolar-magnetized is fixed by performing either press-fitting or adhesion. A projected annular portion 74 is formed in a central portion of the rotor frame 72, and the shaft 71 is directly press-fitted thereinto. In this manner, a rotor assembly 75 is configured.
Numeral 76 denotes a bracket, in which a burring process is applied on a central portion of a steel plate so that a bearing housing is formed and a mounting-base function is integrated. A bearing 77 for rotationally supporting the shaft 71 is press-fixed inside a burring portion of the bracket 76. A stator core 78, which is wound with a stator coil 79 around an iron core via resin insulation, is press-fixed in an outer portion of the burring portion of the bracket 76. At least a part of a circuit for driving and controlling the motor is mounted on a printed circuit board 80, and the printed circuit board 80 is adhered and fixed via a double-side adhesive tape onto a planar portion of the bracket 76. An end of the stator coil 79 is wired on the printed circuit board 80. In this way, a stator assembly is constructed.
Numeral 81 denotes a disengagement-preventing piece for preventing thrust-directional disengagement of the rotational assembly, i.e., the rotor assembly 75, where the disengagement-preventing piece 81 is formed through metal-press processing and is press-fitted onto one end of the shaft 71. Numeral 82 denotes a bottom plate holding a thrust-directional load of the rotor assembly 75 and the bottom plate 82 is press-fitted and fixed at a burring-portion entrance of the bracket 76 via a thrust plate 83 formed of an abrasion-resistant resin.
As described above, the shaft 71 is directly press-fitted in the projected annular portion 74 positioned in the central portion of the rotor frame 72. Thus, the connection between the shaft and the frame is simplified and secured.
However, there are tendencies in which the overall size and the thickness are reduced for brushless motors that are used for information-recording and reproducing devices, such as compact disks, video disks, or magnetic disks, or brushless motors that are used for devices rotationally driven with a load such as a rotational polygon mirror being mounted. To meet requirements in the tendencies, however, when a projected annular portion of a rotor frame and a rotor boss that are connected to a shaft are reduced in length, the difficulty increases in maintaining the strengths of the connected portions.
In addition, in a technique for directly press-fitting, for example, the projected annular portion of the rotor frame onto the shaft, the precision of the rotor assembly depends on the precision of each component with the projected annular portion of the rotor frame. However, in the tendency requiring a higher-speed operation of an information-recording/reproducing device, such as a compact disk, a video disk, or a magnetic disk, the strictness of precision is increasing year by year in precision regarding deflective rotation of a rotational unit for a turntable and a rotor frame of a brushless motor. The strictness of the aforementioned precision is also increasing for a rotational unit such as a rotor boss of a brushless motor used for mounting, for example, a rotational polygon mirror. The conventional connections between a shaft and a rotor frame and between a shaft and a rotor boss therefore encounter difficulties in satisfying the requirements for high precision regarding the deflection.
Furthermore, it is increasingly necessary to obtain a high precision of circumferential portions of the projected annular portion of the rotor frame and the outer diameter portion of the rotor boss. The aforementioned precision is important to perform high-precision mounting of a clamping mechanism that is used for self-clamping an information-recording/reproducing disk such as a compact disk, a video disk, or a magnetic disk, or a rotational polygon mirror that is to be mounted onto the rotor boss.
However, problems are caused in performing accurate positioning and mounting operation because of variations in the outer diameters according to plastic deformation. The plastic deformation occurs on the circumferential portions of the projected annular portion of the rotor frame, the outer diameter of the rotor boss, or the like when the shaft is press-fitted.
In addition to the above-described conventional example, Japanese Utility Model Unexamined Laid-Open Publication No. 63-29369 (published in 1988) discloses another example a configuration of which is shown in FIGS. 9A, 9B, 9C, and 9D.
In this example, the configuration includes an annular groove 91 and a groove 93, as shown in FIGS. 9A, 9B, 9C, and 9D. The annular groove 91 is circumferentially formed on a rotational shaft 90. The groove 93 in the rotational-shaft direction is formed on a bore cylindrical wall of a rotational unit 92 provided adjacent to the annular groove 91. An adhesive 94 is filled into a gap between the annular groove 91 and the groove 93 formed in the direction of the rotational shaft, and the adhesive is then cured. In this way, the configuration is arranged such that the rotational shaft 90 and the rotational unit 92 are connected together to integrally rotate. By this arrangement, the configuration enables the implementation of a rotational unit that allows long-term stable quality to be maintained without an increased number of components, that facilitates assembly, and that produces reduced vibrations.
However, the above configuration requires the process of forming the annular groove. Furthermore, the configuration requires the annular groove to be formed in the rotational-shaft direction on the bore cylindrical wall. The configuration thus requires the complicated grooves to be formed. This creates a problem in that the configuration is not economically advantageous.
When the shaft and the rotor frame are connected by using the adhesive, the centers thereof may deviate from each other because of the gap for adhesion. This deviation causes radial deflections on a clamping mechanism that is used for self-clamping an information-recording/reproducing disk (such as a compact disk, a video disk, or a magnetic disk), a rotor boss that is used for mounting a rotational polygon mirror, or the like. For this reason, a problem occurs in that a load member, such as a compact disk, a video disk, a magnetic disk, or a rotational polygon mirror, causes decentering with respect to the rotational center. During high-speed rotation of the rotor assembly, the decentering causes unbalanced rotation, and the unbalanced rotation causes great vibrations.
Another example is disclosed in Japanese Patent Unexamined Laid-Open Publication No. 8-192285 (published in 1996). In this case, the configuration is arranged such that a rotational shaft is inserted through an insertion hole of a rotor in a manner of a transition fit (i.e., intermediary fit) or a clearance fit (i.e., loose fit). Then, a laser beam is converged on a boundary portion between the insertion hole of the rotor and the rotational shaft to weld the boundary portion. Thereby, the insertion hole of the rotor and the rotational shaft are integrated at the boundary potion. Accordingly, the configuration enables the rotational shaft to be accurately fixed in the center of the rotor without requiring a press-fitting operation that causes deformation of the rotational shaft.
In this arrangement, however, a problem is caused in the method such that, since the insertion hole of the rotor and the rotational shaft are connected with the transition fit or the clearance fit, the centers thereof may deviate from each other because of the gap. This deviation causes radial deflections on a clamping mechanism that is used for self-clamping an information-recording/reproducing disk (such as a compact disk, a video disk, or a magnetic disk), a rotor boss that is used for mounting a rotational polygon mirror, or the like. This method causes another problem such that, because of the transition-fit or clearance-fit engagement between the insertion hole of the rotor and the rotational shaft, the insertion hole of the rotor and the rotational shaft are inserted and welded on jig facilities. This results in complicated jig facilities and the use of laser-emitting devices.
An object of the present invention is to solve the above-described problems involved in the conventional connection structure between the rotor frame and the shaft of the brushless motor and the connection between the rotor boss and the shaft of the brushless motor. That is, the present invention is presented to solve the problems of requirements for higher connection strengths while the connection lengths are reduced.
In addition, another object of the present invention is to solve the above-described problems in the connection between the rotor frame and the shaft of the brushless motor and the connection between the rotor boss and the shaft of the brushless motor; that is, the present invention satisfies the requirements for the deflective-rotation precision while the device-operation speed is increased.
Still another object of the present invention is to solve the problem of outer-diameter variations that occur according to the plastic deformation in the circumferential portions of, for example, the projected annular portion and the rotor boss. The plastic deformation is caused by the press-fitting operation.
Furthermore, by solving the problem of variations in the outer diameter, the present invention is able to provide a motor capable of rotating a load member, such as a disk or a rotational polygon mirror, with a high degree of precision.
To solve the above-described problems and to achieve the aforementioned objects, a first aspect of the present invention provides a brushless motor which comprises: a rotor assembly which includes a substantially cylindrical rotor frame, a magnet that is concentrically disposed in the rotor frame to form a cylindrical spacing, and a shaft having one end fixed in a rotational center of the rotor frame; and a bearing for supporting the rotor assembly. The rotor frame has a projected annular portion in a central portion thereof. The projected annular portion has a small-bore portion and a large-bore portion in a bore thereof, wherein an axial length L1 of the small-bore portion is in a range of Dxc3x970.05xe2x89xa6L1xe2x89xa6Dxc3x970.20 where D represents the diameter of the shaft.
According to the first aspect of the present invention, the length of the small-bore portion positioned on the bore side of the projected annular portion is arranged so as to be selected in an appropriate range to allow the shaft to be press-fitted and connected. Thus, since the press-fitting strength immediately after the press-fit connection can be maintained, therefor to a subsequent step can be performed immediately after the press-fitting connection.
In this arrangement, since the upper limit is specified for the length of the small-bore portion, no case occurs in which an excessively high press-fit load is applied. This enables a press-fitting step to be implemented with a simple tool.
In addition, the configuration may be arranged such that, with respect to the axial length L1 of the small-bore portion of the rotor frame, an axial length L2 of the projected annular portion formed in the central portion of the rotor frame may be in a range of L2xe2x89xa7L1xc3x972. The specific range is appropriate to allow the strength of the connection portion and deflection precision to be compatible.
In a case where the length is equal to or longer than the lower limit in the specified range, the connection strength either between the shaft and the rotor frame or between the shaft and the rotor boss can be maintained. This case is suitably subjected to a light press-fitting step. In a case where the length is equal to or less than the upper limit in the specified range, the connection strength either between the shaft and the rotor frame or between the shaft and the rotor boss can be set to be relatively high. This case is suitable for an assembly step in which the production tact is fast. Furthermore, when the axial length L2 of the projected annular portion is set sufficiently long in relation to the length L1 of the small-bore portion, a sufficient length of an adhesive portion can be obtained. Accordingly, sufficient adhesion strength can be secured, and consequently, the final strength of the connection portion can be increased.
A second aspect of the present invention provides a production method for a brushless motor having a rotor assembly that includes a shaft, a rotor frame having a projected annular portion in a central portion thereof where the projected annular portion has a small-bore portion and a large-bore portion in a bore thereof, and a magnet is concentrically disposed in the rotor frame and that forms a cylindrical spacing. The method comprises the steps of: press-fitting one end of the shaft into the small-bore portion; and filling an adhesive into a gap between the large-bore portion and the shaft to thereby connect the rotor frame to the shaft. According to the above-described production method for the brushless motor, the rotor frame is connected to the shaft, so that the rotor assembly of the brushless motor is produced.
A third aspect of the present invention provides a brushless motor which comprises: a rotor assembly which includes a shaft, a rotor boss having a central circular bore in which the shaft is inserted, a rotor frame fitted to the rotor boss, and a magnet that is concentrically disposed in the rotor frame so as to form a cylindrical spacing; and a bearing for supporting the rotor assembly. The rotor boss has a small-bore portion and a large-bore portion in the bore thereof, wherein an axial length L1 of the small-bore portion is in a range of Dxc3x970.05xe2x89xa6L1xe2x89xa6Dxc3x970.20 where D represents the diameter of the shaft.
According to the third aspect of the present invention, the shaft is press-fitted and connected to the small-bore portion positioned in the bore of the rotor boss. In this arrangement, since the press-fitting strength immediately after the press-fit connection can be maintained, handling in a subsequent step can be performed immediately after the press-fitting connection. Furthermore, since the upper limit is specified for the length of the small-bore portion, no case occurs in which an excessively high press-fit load is applied. This enables a press-fitting step to be performed with a simple tool.
In the above-described third aspect of the present invention, the configuration may be arranged such that, with respect to the length L1 of the small-bore portion of the rotor boss, an axial length L2 of the annular bore portion formed in the central portion of rotor boss is in a range of L2xe2x89xa7L1xc3x972. The specified range is appropriate to allow the strength of the connection portion and deflection precision to be compatible. In a case where the length is equal to or longer than the lower limit in the specified range, the connection strength either between the shaft and the rotor frame or between the shaft and the rotor boss can be maintained. This case is suitably subjected to a light press-fitting step.
In a case where the length is equal to or less than the upper limit in the specified range, the connection strength either between the shaft and the rotor frame or between the shaft and the rotor boss can be set to be relatively high. This case is suitable for an assembly step in which the production tact is fast. Furthermore, when the axial length L2 of the projected annular portion is set sufficiently long in relation to the length L1 of the small-bore portion, a sufficient length of an adhesive portion can be obtained. Accordingly, sufficient adhesion strength can be secured, and consequently, the final strength of the connection portion can be increased.
A fourth aspect of the present invention provides a production method for a brushless motor having a rotor assembly which includes a shaft, a rotor boss having a central circular bore in which the shaft is inserted, a rotor frame fitted to the rotor boss where the rotor boss has a small-bore portion and a large-bore portion in the bore thereof; and a magnet is concentrically disposed in the rotor frame to form a cylindrical spacing. The method comprises the steps of: press-fitting one end of the shaft into the small-bore portion; and filling an adhesive into a gap between the large-bore portion and the shaft to connect the rotor boss to the shaft. According to the above-described production method for the brushless motor, the rotor frame is connected to the shaft, so that the rotor assembly of the brushless motor is produced.
A fifth aspect of the present invention provides a brushless motor which comprises: a rotor assembly which includes a shaft, a rotor boss having a central circular bore in which the shaft is inserted, a rotor frame fitted to the rotor boss, and a magnet that is concentrically disposed in the rotor frame to form a cylindrical spacing. The rotor boss comprises a small-bore portion and a large-bore portion in the bore thereof, and one end of the shaft is press-fitted into the small-bore portion. An axial length L1 of the small-bore portion is in a range of Dxc3x970.05xe2x89xa6L1xe2x89xa6Dxc3x970.20 where D represents the diameter of the shaft, and wherein a connection boundary portion between the small-bore portion and the shaft or a connection boundary portion between the large-bore portion and the shaft is welded with laser beams to thereby connect the rotor boss to the shaft.
By this construction, the length of the small-bore portion positioned on the bore side of the rotor boss having the circular bore is arranged so as to be selected in an appropriate range to allow the shaft to be press-fitted and connected. According to this arrangement, since the press-fitting strength immediately after the press-fit connection can be maintained, handling in a subsequent step can be performed immediately after the press-fitting connection.
Furthermore, a connection boundary portion between the small-bore portion and the shaft or a connection boundary portion between the large-bore portion and the shaft is welded using laser beams to thereby connect the rotor boss to the shaft. This enables the precision to be maintained, and concurrently, enables the final strength of the connection portion to be increased.
A sixth aspect of the present invention provides a production method for -a brushless motor which includes a rotor assembly comprising a shaft, a rotor boss having a central circular bore in which the shaft is inserted, a rotor frame fitted to the rotor boss where the rotor boss has a small-bore portion and a large-bore portion in the bore thereof, and a magnet concentrically disposed in the rotor frame so as to form a cylindrical spacing. The method comprises the steps of: forming a small-bore portion and a large-bore portion in the bore of the rotor boss; press-fitting one end of the shaft into the small-bore portion; welding one of a connection boundary portion between the small-bore portion and the shaft and a connection boundary portion between the large-bore portion and the shaft with laser beams to thereby connect the rotor boss to the shaft.
According to the above-described production method for the brushless motor, the rotor boss is connected to the shaft, so that the rotor assembly of the brushless motor is produced.
In the above-described sixth aspect of the present invention, the configuration may be arranged such that the laser welded portion of the connection boundary portion may be an overall circumference of the shaft. In this way, different from a case where partial spot welding is performed, welding is performed entirely along the overall circumference of the shaft. Thereby, sufficient weld strength can be secured, and the final strength of the connection portion can be increased.